Bone snapping to control bone while making an Inverse Kinematic Rig
Your problem has a very simple answer. When ever you add IK control to a rig, the  default chain length is usually $0$ and the bone tries to point at the rig's origin, thus creating some weird posture.
You can solve this by adjusting the chain length to the number of bone you would like to be influenced by the inverse kinematics(IK).
Try $1$ or $2$ and get a feel of what work best for the rig.